I have found that animals treated acutely with psychotic agent methylene dioxymeth-amphetamine (MDMA, "Ecstasy") undergo a number of neurochemical alterations in the brain. Acute administration of MDMA results in a rapid decrease in the levels of serotonin and its metabolites in the brain. In addition, dopamine concentrations rapidly increase. These alteractions persist for up to 1 week after administration. In response to these changes in transmitter levels I have seen a selective and persistent increase in serotonin type-1 receptor binding, while dopamine type-1 receptors show a marked decrease in binding. No change is seen in seratonin type-2 receptor binding. These results indicate that MDMA administration may result in neurotoxicity.